The objectives of this proposal are to analyze the specific plasma membrane lipids of isolated rat adipocytes derived from normal and insuling-resistant diabetic state, and to determine how alterations of these lipids are related to biological function in terms of hexose transport and insulin binding. Adipocyte plasma membranes will be isolated by sucrose density centrifugation and analyzed by thin layer and gas-liquid chromatography. Lipid alterations in the normal and diabetic state will be carried out by interacting fat cells with artificially generated unilammelar vesicles (liposomes) under conditions in which the vesicle lipids become incorporated into the fat cell plasma membrane by a vesicle-cell fusion process. Vesible lipid composition will be varied to include both naturally occurring phospholipids and/or defined acyl chain phospholipids. The extent of the alterations will be quantified by using radiolabeled phospholipids of known specific activities and the fate of the lipid exogenously introduced into the cell membrane will be monitored by the biochemical fractionation of adipocytes. The biological effect of these alterations will be assessed by measuring insulin binding using 125I-labeled insulin under a variety of conditions and by monitoring 2-deoxy-glucose transport. These parameters will be studied in adipocytes from both normal rats and those which are insulin-resistant due to administration of streptozotocin or obesity. Finally, the possible mechanisms by which phospholipids affect insulin action will be analyzed by reconstitution of the adipocyte glucose transport system or the insuling receptor into physically and chemically defined phospholipid vesicles.